Incidence and Risk Factors of Epilepsy Among Older Adults in the US Medicare Population.

Importance: Geographic variation in epilepsy incidence among older adults may reflect contextual risk factors and point to opportunities for targeted prevention. However, privacy constraints and sparse case counts have historically limited small-area analyses. Objective: To map incident epilepsy among older adults at the smallest geography permissible by privacy constraints and identify contextual social and environmental determinants associated with high-incidence areas. Design, Setting, and Participants: This cohort study examined Medicare administrative claims from 2016 to 2019 for all counties in the contiguous United States. A random sample of 4 999 999 Medicare Fee-for-Service beneficiaries 65 years or older with non-Hispanic Black and Hispanic beneficiaries oversampled at rates of 1.50 and 1.75 times their representation in the study population. Beneficiaries with incident epilepsy were identified by claims criteria and codes from the International Statistical Classification of Diseases and Related Health Problems, Tenth Revision, in 2019 and had no epilepsy claims during the period 2016 to 2018. Data were analyzed from January to March 2025. Exposures: Area-level social and environmental determinants of health (SEDH), obtained from publicly available sources and linked to beneficiaries' residences. Main Outcomes and Measures: The outcome was area-level epilepsy incidence rate in 2019. To comply with data privacy requirements, the Max-P regionalization method was used to aggregate 3108 counties into 692 "MaxCounties," each containing at least 11 incident cases. Incidence rates per 100 000 persons were mapped. Associations between SEDH variables and epilepsy incidence were estimated using random forest and multivariable logistic regression. Results: Among 4 817 147 beneficiaries, 20 263 incident epilepsy cases were identified in 2019 (mean [SD] age, 78.7 [7.5] years; 54.6% women). Incidence rates across MaxCounties varied more than 10-fold (range, 141-1476 per 100 000). In random forest models, higher incidence was associated with insufficient sleep, heat index, physical inactivity, uninsured rate, proportion of non-Hispanic Black residents, and obesity prevalence. In multivariable regression, MaxCounties in the highest tertile for insufficient sleep had nearly double the odds of high epilepsy incidence compared to the lowest tertile (odds ratio [OR], 1.99; 95% CI, 1.10-3.60). Lack of household vehicle access was similarly associated with high incidence (OR, 1.93; 95% CI, 1.16-3.25). Conclusions and Relevance: Our findings highlight the spatial heterogeneity of epilepsy burden in the US Medicare population and underscore the importance of contextual SEDH factors, such as sleep, mobility, and infrastructure, in shaping disease patterns. These insights may help guide targeted public health interventions and resource allocation.